Criminals were paid more than $6 million in wages while living behind bars last year for jobs such as cleaning the prison laundry or kitchen and farming, engineering and concrete production jobs outside the perimeter fence.

Figures released to the Herald under the Official Information Act also showed that more than $23 million was spent on rehabilitation programmes such as life skills and drug treatment, $5.6 million was spent on psychiatrists and $2.1 million on chaplaincy services.

Of the 8067 inmates during the last financial year, half were employed to work either within the prison or as part of one of two specialist programmes within the community.

Corrections general manager of rehabilitation and reintegration services Alison Thom said the idea was to increase the chances of prisoners obtaining sustainable employment when they were released.

Research showed it had reduced offending.

For the year to June 2009, there were 1576 inmates employed in prison-based work, which mainly involved cleaning units.

For the 2.24 million hours completed, prisoners received about $675,000 in total, which was about 20c to 40c an hour.

And there were 2230 low-security prisoners involved in Corrections Inmate Employment last year and they earned $1.69 million in total, about 40c an hour.

This involved working and trade training in a variety of roles including as part of one of the 140 "business-like" industries operating within the prison such as farming, forestry, timber processing, engineering, horticulture, concrete production, building refurbishment, distribution and joinery.

Some supervised groups of inmates work with councils or businesses on work contracts outside the prison.

"These activities aim to assist prisoners to establish work habits and skills in a non-commercial environment," Ms Thom said.

"The purpose of the incentive is to motivate prisoners to improve work-related skills, which will enable them to secure meaningful employment in society upon their release from prison."

And 150 low-security prisoners, who were approaching the end of their sentences, were employed as part of the Release to Work programme.

They were released into the community daily to work for private employers and were paid market wages.

Corrections did not reveal how much the prisoners would have been paid in total but if each earned the minimum wage of $12.75 an hour, they would have earned at least $4 million.

Ms Thom said a background check was made on employers. Suitability of the type of work, location and other staff was also assessed.

Many prisoners continue in the employment once released.

Prisoners on the programme are required to pay 30 per cent of their wages (up to $250) back to Corrections to cover the cost of their imprisonment in an attempt to get them used to making regular payments for accommodation.

Money is also deducted for court-imposed fines and child-support payments. Remaining money is put into an account they can access once they are released.

Sensible Sentencing Trust spokesman Garth McVicar said it was not fair on taxpayers that their money was going towards paying the wages of criminals.

"We knew they were getting paid but we didn't know it was that much, I'm quite astonished by that and I'm sure the majority of New Zealanders will be too.

"Some of their victims are out of pocket - there was $90 million-odd in unpaid fines and reparation wiped last year."

Mr McVicar said he agreed prisoners should work but suggested Corrections follow a system similar to that in Europe.

All inmates had to work but while serving the first third of their sentence were not paid a wage, he said.

In the second third they earned a small wage, but could only work behind prison bars. And in the final stage of their sentence they could be released to work.

Jail expenses

* $6.3 million was paid in wages to 3956 prisoners last year.

* $2.1 million spent on chaplaincy for prisoners.

* $5.6 million on psychiatrists.

* $2.69 million on motivational programmes for 1365 prisoners.

* $7.87 million on special treatment units (sex offender treatment, drug treatment, youth anti-social behaviour programme, faith-based unit) for 688 prisoners.

* $5.86 million on medium-intensity rehabilitation programmes (Maori therapeutic, relapse prevention) for 1379 prisoners.

* $7.54 million on education (skills programmes and secondary education) for 2158 prisoners.

* $4.12 million on reintegration programmes (living, parenting and budgeting skills) for 1103 prisoners.

* Total $44.26 million.